The present invention generally relates to vehicle suspensions. More particularly, the present invention relates to vehicle air suspension systems that include an armored pneumatic spring, or air spring useful for protecting the air spring from small arms fire, shrapnel from explosions and other debris. The pneumatic suspension may include an air strut assembly comprising an air cylinder and damper, which may be referred to as air spring assembly or strut assembly. Prior strut assemblies have included a flexible air spring made of rubber wherein the air spring includes a flexible rubber membrane that expands as the strut is loaded. Typical air springs of this type with a flexible rubber membrane provide a relatively low spring rate. As a result, additional spring rate and roll stiffness has typically been required to be added to the vehicle, e.g., often in the form of an additional, independent mechanical coil spring to meet vehicle handling and stability objectives. Therefore, when using air springs with flexible or expandable membranes, an ‘anti-roll bar’ or ‘sway bar’ has often been utilized as the mechanism to achieve the desired auxiliary roll stiffness.
In typical air springs with a flexible membrane, the operating pressures that may be utilized are limited because of the current limitations on flexible membrane and rubber construction. Thus, the typical operating pressure at normalized ride height is limited to 80-100 psi, up to 120 psi, with maximum pressure at full compression at around 200 psi. It is known that by increasing the effective spring rate of the strut assembly, the vehicle may achieve a higher ride frequency, and increased roll performance and lateral stability performance. In particular, when the effective spring rate of the strut at the designed ride height is increased, the need for auxiliary anti-roll devices may be eliminated.
In some applications using an air spring with a flexible membrane, a coil spring may be added to increase the effective spring rate of the strut. However, to achieve a desired effective spring rate at the designed ride height, the strut may require a larger spring, a larger volume of air (and thus a flexible membrane with a larger diameter) or a combination of both. In many applications, however, the space constraints, or limited footprint available for a strut, do not allow for an air spring with a flexible membrane even when combined with a coil spring to achieve the desired increased effective spring rate at the designed ride height of a vehicle because of the increased size of the strut required to achieve the desired effective spring rate.
Therefore, in some applications it would be desirable to provide a strut capable of operating at increased operating pressures, to achieve a desired increased effective spring rate at the designed ride height that fits within existing space constraints. In addition, it would be desirable to provide a strut having an increased effective spring rate. For example, in some applications it may be desirable to provide a strut having an effective spring rate high enough so that the need for auxiliary roll resisting devices such as an anti-roll bar is not required to achieve the desired vehicle roll resistance and lateral stability. Furthermore, it would be desirable to provide an air strut that does not expand when subjected to a load.
In addition, vehicle suspensions are also used with military vehicles. Military vehicles are often used in dangerous environments and may be subjected to small arms fire, shrapnel from exploding devices, and other debris encountered in harsh environments. Pneumatic air springs having a flexible rubber membrane are vulnerable to suffering damage from small arms fire, shrapnel from explosions and miscellaneous debris encounter in harsh operating conditions. Furthermore, because the flexible rubber membrane expands when a load is applied, it is difficult to provide a protective layer of armor around the periphery of the flexible rubber membrane, although desirable. Thus, a pneumatic air spring that has a non-expandable outer shell is a better candidate for providing a protective layer of armor thereon.